1. Field of the Invention
The present invention relates to reciprocating piston type compressors such as those employing swash plates, and more particularly, to reciprocating piston type compressors that enable reduction of vibration and noise.
2. Description of the Related Art
Piston type compressors are generally mounted on vehicles to air-condition passenger compartments. A typical piston type compressor has a crank chamber, which is defined in a housing, and a drive shaft, which is supported in the crank chamber. The drive shaft is connected to a vehicle engine by a clutch. A plurality of cylinder bores extend parallel to and about the drive shaft in a cylinder block, which constitutes part of the housing. A piston is accommodated for reciprocation in each cylinder bore. A compression chamber is defined in each cylinder bore by the piston. A swash plate is fixed to the drive shaft and rotates integrally with the shaft. Rotation of the swash plate is converted to linear reciprocation of each piston. The reciprocation of each piston compresses the refrigerant gas in each compression chamber.
The compressing motion of each piston causes a compression reaction to act on the piston. The compression reaction is transmitted to the drive shaft through the swash plate and causes fluctuation of the drive shaft torque. The torque fluctuation produces torsional vibration between the drive shaft and the clutch. This generates vibrations and noise. When analyzing the sum of the torque fluctuations, that is, the sum of each compression reaction produced in the compression chambers, using a fast Fourier transform (FFT), it is apparent that the torque fluctuation occurs cyclically. It is also apparent that the torque fluctation includes a wide variety of frequency components ranging from zero cycles to a large number of cycles. Among the frequency components, the main component is the n cycle component, which corresponds to the number (n) of the cylinder bores. The n cycle component corresponds to the vibration component that occurs cyclically n number of times during a single rotation of the drive shaft. For example, a ten cycle component corresponds to the vibration component that takes place cyclically ten times during a single rotation of the drive shaft. When the frequency of the n cycle component is close to the vibration frequency of the compressor and its peripheral equipment, resonance phenomena produces noise that may be transmitted to the passenger compartment.
Japanese Unexamined Utility Model Publication No. 1-160180 describes a variable displacement compressor employing a wobble type swash plate. The compressor is provided with five cylinder bores. The distances between adjacent cylinder bores are not equal. Furthermore, the dead volume (the volume of the compression chamber when the piston is located at the top dead center) in the compression chamber of one of the cylinder bores differs from the dead volume in the other cylinder bores. The top end of one of the pistons is shortened for a predetermined length to increase its associated dead volume. This alters the volume and pressure of the compression chamber. The increase in the dead volume reduces the compression reaction produced in the compression chamber and enables the sum of the compression reactions acting on the swash plate to always be constant. Therefore, the swash plate rotates smoothly due to the decrease in the torque fluctuation of the drive shaft. As a result, the generation of torsional vibration and noise is decreased.
However, the compressor of the above publication merely changes the dead volume of one or more cylinder bores to decrease the torsional vibrations and noise of the compressor. In addition, the above publication does not teach how to further decrease the torque fluctuation of the drive shaft. Therefore, when applying the device of the publication to various types of compressors, the decrease in the torque fluctuation of the drive shaft may be insufficient. Thus, the generation of vibration and noise may not be adequately suppressed.